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D. L. Blaney, J. D. Goguen, G. J. Veeder, D. L. Matson, T. V. Johnson (NASA JPL)
Ground based telescopic observations of Europa at 8.7, 12.5, and 20 \mum were taken between July 13 and November 4, 1998 at the NASA Infrared Telescope Facility. Europa's thermal emission has a relatively large amplitude light curve with a maximum around 345 W longitude and a minimum around 100 W longitude. The amplitudes of the observed emission was 0.0505 to 0.0111 Wm-2\mum-1 at 8.7 um; 0.0526 to 0.189 Wm-2\mum-1 at 12.5 um; and 0.185 - 0.413 Wm-2\mum-1 at 20 \mum. A single eclipse was observed at roughly 350 W longitude with emission levels of 0.0055 Wm-2\mum-1 at 8.7 \mum, 0.020 Wm-2\mum-1 at 12.5 \mum, and 0.114 Wm-2\mum-1at 20 \mum.
We modeled Europa's infrared orbital light curve for two cases using a spatially resolved albedo map based on Voyager data. The best fits for a single thermal inertial was 8x10-4 cal/(cm2s1/2K) but this model was not able to match the amplitude of the light curve. Good fits for the 12.5 and 20 \mum curves were made using two thermal inertias tied to albedo. High albedo (i.e. >0.6) units had values of 1.4x10-3 cal /(cm2s1/2K) while a value of 4.0x10-4 cal/(cm2s1/2K) was used for the low albedo units. However, the measured thermal emission at 8.7 \mum is in excess over that predicted by the models. Also, the thermal emission observed in eclipse at all wavelengths was larger than expected from these preliminary thermal models. Further modeling and the implications of these results for Europa's thermophysical properties, global heat flow, and resurfacing will be presented.
The author(s) of this abstract have provided an email address for comments about the abstract: blaney@scn1.jpl.nasa.gov